Two oscillatory components detected by forced splitting of the sleep-wake cycle in humans

Am J Physiol Regul Integr Comp Physiol. 2023 Oct 23. doi: 10.1152/ajpregu.00094.2023. Online ahead of print.ABSTRACTThe sleep-wake cycle of human subjects was artificially split into two episodes by imposing an 8-h light and 4-h dark cycle (LD 8:4) twice a day for 7 days, which was followed by a 3 day free-running session. Sleep was permitted only in the dark period. The subjects in the ordinary group were exposed to ordinary light (ca. 500 lux) in the 8-h light period, and those in the bright light group to bright (ca. 5,000 lux) and ordinary light alternatively with bright light after the 1st dark period (24:00 - 4:00 h). Split sleeps persisted in the free-running session with the major episode around the 1st dark period and the minor episode around the 2nd dark. By contrast, circadian melatonin rhythm in the free-running session significantly phase-delayed in the ordinary light group, but phase-advanced in the bright light group, keeping the melatonin rhythm un-split. The length of nocturnal melatonin secretion (NMS) was significantly shortened in the bright light group. Interestingly, the falling phase of NMS advanced significantly further than the rising phase. Such a difference was not detected in the ordinary light group. Similar differences were observed in the body temperature rhythm. These findings indicated oscillatory mechanisms underlying split sleeps distinct from the circadian pacemaker, and suggested an involvement of different circadian oscillators in the ris...
Source: American Journal of Physiology. Regulatory, Integrative and Comparative Physiology - Category: Physiology Authors: Source Type: research